1. Field of Invention
The present invention relates to wireless datacast systems, and in particular to wireless datacast systems having multiple wireless datacast channels.
2. Related Art
Existing terrestrial AM and FM commercial radio (wireless) stations are converting from real-time analog to real-time digital radio signal formats (digital audio broadcasting (DAB)). In the United States, commercial broadcasters are adopting the In-band On-Channel system (IBOC), currently developed as iDABT(trademark) by the iBiquity Digital Corporation, Columbia, Md., for DAB conversion. The IBOC system allows commercial broadcasters to retain their present government-licensed frequency spectrum allocation during the DAB transition.
IBOC systems are known and may be either all digital or hybrid. In the hybrid IBOC system, commercial broadcasters use a portion of their licensed frequency spectrum for the traditional analog radio signal transmission (e.g., AM or FM radio signal) of a primary (real-time) program while contemporaneously transmitting a DAB version of the primary program in upper and lower sideband areas of the analog carrier within the station""s allocated spectrum. This contemporaneous analog and digital program transmission allows listeners to continue to use existing receivers during the industry transition to all digital broadcasting. Hybrid IBOC receivers tuned to a Hybrid IBOC station extract program information from the digital signal, if available. If the digital signal becomes unavailable (e.g., blocked by an obstacle) the receiver senses the digital signal loss and begins to extract the program information from the analog signal. The Hybrid IBOC is intended as an intermediate stage in the transition to all digital IBOC.
In DAB, each broadcast channel is typically divided into a primary channel and at least one ancillary data channel. DAB transmission of the primary program (via a primary channel) typically requires less bandwidth than is available in the sideband spectrum areas of a particular station""s broadcast channel. Therefore, unused portions of the digital broadcast spectrum are allocated for datacast transmission (via an ancillary data channel). Datacasting is the transmission of information (e.g., audio, video, text, financial data, paging information) in an ancillary data channel having a bandwidth too narrow to support broadcast of a second primary, real-time, DAB program broadcast within the station""s spectrum allocated by government regulation (station""s broadcast channel).
The available datacast channel bandwidth depends on the bandwidth required for the associated main program DAB broadcast. If a commercial broadcaster desires xe2x80x9cCD-likexe2x80x9d audio quality (i.e., relatively high audio fidelity), more DAB bandwidth is required with a consequent decrease in available datacast bandwidth. If a commercial broadcaster requires relatively less audio fidelity (e.g., for a talk radio program) for a primary channel there is a consequent increase in available ancillary data channel bandwidth. For example, the maximum net digital capacity on a United States commercial FM station supported by the Hybrid IBOC design for FM broadcast systems is 144 kilobits per second (144 kbps=18 kilobytes per second or 18 KBps). A station transmitting high quality audio might reserve 96 kbps for audio and reserve 48 kbps (6 KBps) for data services (datacasting). A station with lower audio quality requirements (e.g., for talk format program) may set the digital audio (primary channel) capacity at 64 kbps and the ancillary data channel capacity at 80 kbps (10 KBps). These are maximum data rates and do not include overhead information requirements such as forward error correction (FEC) (e.g., Reed-Solomon encoding). Under some Hybrid IBOC designs, for example, FEC requires 24 kbps for each side band.
In addition to AM and FM commercial stations, digital radio signal transmission is used for other commercial broadcast systems. For example, digital television broadcast systems are being deployed in the United States and in Europe. Satellite digital audio radio (SDAR) systems, such as proprietary systems developed by Sirius Satellite Radio Inc., New York, N.Y., and by XM Satellite Radio Inc., Washington, D.C., are being developed and introduced. All digital radio signal broadcast systems have excess bandwidth capacity in each station""s channel that may be allocated for datacasting.
Existing analog AM and FM commercial stations support datacasting in subcarriers of the main analog program carrier signal. This datacasting capacity is used to support information delivery systems such as the on-demand information system developed by Command Audio Corporation, Redwood City, Calif. The portable receiver in this illustrative on-demand system stores received programs for later output (playback) to the user. In the Command Audio Corporation system, the net data rate after convolutional encoding and FEC is 8.2 kbps.
A disadvantage of both existing analog and digital radio broadcast systems is that the ancillary data channel capacity, typically in a single ancillary data channel controlled by a unique commercial broadcast entity, is limited. Thus, some information delivery systems that require or can use additional datacast capacity are not possible. What is required is a way to provide increased data carrying capacity for information delivery systems within the constraints imposed by existing and future digital broadcast systems.
A network datacast system includes a plurality of transmission facilities, each transmission facility broadcasting a unique wireless signal in one or more channels. Each channel is allocated bandwidth for primary programs (primary channel) and for ancillary datacast programs (ancillary data channel). Each transmission facility in the network receives primary programs from one or more media studios. Each transmission facility also receives ancillary programs from a network datacast center. The transmission facilities contemporaneously broadcast the received ancillary programs in the ancillary data channel portions of the broadcast channels.
A network datacast receiver receives the wireless signals from the transmission facilities and contemporaneously extracts the ancillary programs from the received signals. The receiver subsequently stores the received ancillary programs for output to the user at the user""s request.